Recently, as the noise generated by the car mechanism and body becomes reduced, the percentage of the noise generated by the tire increases. Therefore, there is an increasing demand for a low noise tire.
For reducing the tire noise, it is especially effective to reduce a relatively high frequency noise to which the human ears are sensitive, that is, noise whose frequency range is around 1 kHz.
Air resonance noise is such a high frequency tire noise. Air resonance noise is explained as follows.
In the ground contacting patch of the tire, an air tube is formed by the road surface and a continuous circumferential groove which is provided in the tire tread portion. During running, the air tube is excited by the air flow, a tread deformation or movement, roughness of the road surface and the like, and a noisy sound having a specific wave length which corresponds to two times the length of the air tube is generated. Most tire noise whose frequency range is about 800 to 1.2 k Hz generated by the tire having a circumferential groove is such air resonance noise. The frequency of the air resonance is almost constant independent of running speed.
Since it has been known that air resonance can be prevented by decreasing groove volume, decreasing groove volume and/or the number of circumferential grooves has been employed to reduce air resonance noise. As a result, wet performance such as aquaplaning, wet grip and the like is inevitably decreased.
It is therefore, an object of the present invention to provide a pneumatic tire in which, by using a very wide circumferential groove and continuously changing the conditions of the air resonance during running, the air resonance noise is effectively reduced to decrease the overall noise level without sacrificing wet performance.
The foregoing specific objects and advantages of the invention are illustrative of those which can be achieved by the present invention and are not intended to be exhaustive or limiting of the possible advantages which can be realized. Thus these and other objects and advantages of the invention will be apparent from the description herein or can be learned from practicing the invention, both as embodied herein or as modified in view of any variations which may be apparent to those skilled in the art. Accordingly, the present invention resides in the novel parts, constructions, arrangements, combinations and improvements herein shown described.